This photograph is of an igneous dyke on Anglesey. Molten magma must have forced its way sideways between existing layers and then solidified. The way that molten magma moves under the surface of the Earth is very much to do with physics. It is due to convection cycles in the mantle. I was interested to note that in Brian Cox's series on the Solar System, he attributed the loss of atmosphere on Mars to the cooling and solidifying of its molten core.
